MCP-PMT's are unique in having the capability of 10-micron pixel size, psec-level time-resolution, high gain, and low noise. Recent developments have made possible the coverage of large areas by advances in capillary substrate manufacture, resistive and emissive coatings, and fast economical electronics systems.
A dominant barrier to adoption of MCP-PMT technology is cost. The cost is dominated by the complex one-at-a-time production and assembly process, and by process yield. A typical MCP-PMT commercial fabrication process is much more expensive than the production of conventional PMTs due to the synthesis of the photocathode inside a large vacuum vessel that must be heated to a high temperature, followed by transfer of the cathode inside the vacuum, rather than synthesis in place inside the much smaller photodetector package, as is done with PMTs. The flat planar form-factor of MCP-PMTs prohibits using the same process as for deposition in PMTs; each MCP-PMT has to be assembled inside a tank after the photocathode has been separately deposited on the window. The typical production process for PMTs, in contrast, synthesizes the photocathode inside the detector's glass tube envelope, allowing batch production and consequently a higher yield and lower cost.
Current commercial processes produce MCP-PMT photodetectors with a transmission-mode photocathode. In this geometry, the photocathode is deposited as a film on the vacuum side of the window. The film absorbs the incoming photon, and therefore is better when it is optically thick; however, the electron has to be ejected from the vacuum side, opposite to where the photon enters, and so the efficiency of ejecting a photoelectron is better for a thin film. These conflicting requirements on the film thickness lead to an inherent inefficiency, and a sensitive dependence on film thickness during manufacture, affecting yield. In contrast, a reflection-mode cathode is deposited on a surface facing the incident photon's path; the electron is ejected from the same surface, and since it does not have to traverse the photocathode, the film can be very thick or even non-uniform without any effect on performance. Because the film is thicker, photocathodes in reflection-mode typically have higher Quantum Efficiency (QE) than in transmission-mode.